The present invention relates to an engine cooling apparatus, which cools down an engine by circulating a coolant, and more particularly to an engine cooling apparatus, which controls the flow rate of the coolant that passes through a radiator provided in a coolant circulation passage of the engine.
As a conventional cooling apparatus provided in an engine, the most popular type has been one, which uniformly adjusts a coolant to a temperature of approximately 80xc2x0 by a thermostat irrespective of an operation state of the engine. In order to achieve reduction in friction of the engine, improvement in fuel consumption or knocking performance and others, however, it is confirmed that changing a degree of cooling in accordance with an operation state of the engine (load condition, rotational speed or the like) is effective. Therefore, there have been proposed several cooling apparatuses designed to control a degree of cooling in accordance with an operation state of the engine.
As this type of cooling apparatus, for example, there is an engine cooling apparatus disclosed in Japanese Laid-Open Patent Publication No. 5-179948. This engine cooling apparatus is configured for the purpose of adjusting a temperature of a coolant that circulates in the engine in accordance with the load condition of the engine. That is, this apparatus is designed to set a target temperature of the coolant based on the load condition of the engine and controls a flow rate of the coolant that passes through a radiator in such a manner that a temperature of the coolant that flows on an outlet side of a water jacket reaches this target temperature. More specifically, a temperature difference between an actual coolant temperature detected by a coolant temperature sensor and the target temperature is obtained. Further, an amount of duty change is obtained from this temperature difference by making reference to map data, and a temperature of the coolant that flows on the outlet side of the water jacket is adjusted to the target temperature by controlling a flow regulating valve, which adjusts a flow rate of the coolant passing through the radiator, based on the amount of duty change.
In the prior art engine cooling apparatus in the above patent publication, since the flow regulating valve is merely controlled based on a temperature difference between the actual coolant temperature and the target temperature, there is a problem in the responsibility of the coolant temperature control conducted in order to adjust the coolant temperature to the target temperature. In particular, since the actual coolant temperature deviates from the target temperature in the transition of the operation state of the engine, there occurs a loss in terms of reduction in friction, improvement in fuel consumption or knocking performance and others during the transient operation of the engine.
It is an object of the present invention to provide an engine cooling apparatus capable of improving the responsibility of the coolant temperature control conducted in order to adjust a temperature of a coolant circulating in an engine to a target temperature.
To achieve the above object, the present invention provides an engine cooling apparatus including a circulation passage, a radiator, a flow regulating valve, and a controller. The circulation passage extends through an engine, and coolant flows through the circulation passage. The radiator is provided in the circulation passage and cools coolant passing through the circulation passage. The flow regulating valve regulates the flow rate of coolant flowing through the radiator. The controller controls the flow regulating valve. The controller sets a feedforward term, which corresponds to a basic opening of the flow regulating valve, based on the operation state of the engine. The controller sets a feedback term, which is adjusted such that the engine coolant temperature converges on a predetermined target value. The controller feedback controls the opening of the flow regulating valve based on the feedforward term and the feedback term.
The present invention also provides a method for controlling an engine cooling apparatus, which includes a coolant circulation passage extending through an engine. The method includes: cooling coolant passing through the circulation passage with a radiator provided in the circulation passage; regulating the flow rate of coolant flowing through the radiator with a flow regulating valve; setting a feedforward term based on the operation state of the engine, the feedforward term corresponding to a basic opening of the flow regulating valve; setting a feedback term, the feedback term being adjusted such that the engine coolant temperature, which is the temperature of coolant flowing through the engine, converges on a predetermined target value; and feedback controlling the opening of the flow regulating valve based on the feedforward term and the feedback term.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.